At the present time, machine tools having large rotary members, such as swinging arm robots, are constructed so as to attenuate detrimental effects of reaction forces generated when the rotary members are moved. Typically, a servo motor or the like is mounted to a base of the machine, with the rotary member moved by the motor via a gear or pulley arrangement. When the rotary member is moved, reaction forces of the motor are absorbed into the heavy, well dampened mass of the base, which is generally of rigid cast iron or polymer machine construction and may be further secured to a concrete floor or other heavy foundation to further dampen these reaction forces.
While generally effective, the mass needed to provide damping for these reaction forces is expensive, as is the structure needed to support the mass of the machines. Further, machine accuracy is limited by the mass of the machine and its rigidity due to the fact that reaction forces are attenuated and not eliminated. Further yet, with increasing machining speeds, flexure of the base occurs when heavy loads are applied thereto by the motor, in turn causing machining accuracy to deteriorate proportionally.
The principles governing behavior of rotating bodies, hereinafter denoted as gyroscopic masses, are well understood, and have been used for many years in many forms as sensor elements to provide stabilizing signals for control of various vehicular contrivances, particularly aircraft. In other applications, relatively large gyroscopic masses, known as Control Moment Gyroscopes, (CMG) have been developed and mounted in spacecraft and used to maintain a fixed attitude of the spacecraft through the use of gyroscopic forces. From the 1970's through the present, HONEYWELL CORP. (.TM.) of Phoenix, Ariz. has been a major source CMG technology as well as reaction wheel systems for satellite attitude control. During this time, intensive efforts have been made to refine performance capabilities and reliability of CMG technology. Among these endeavors was the successful development of a magnetically suspended reaction wheel for the Annular Momentum Control Device. For further information on these devices, the reader is directed to the following publications:
1) THE ANNULAR MOMENTUM CONTROL DEVICE by W. W. Anderson. PA0 2) ANNULAR MOMENTUM CONTROL DEVICES by Ball Brothers Research Corp. of Boulder Colo. PA0 3) ANNULAR MOMENTUM CONTROL DEVICES, APPLICATION TO A LARGE SPACE TELESCOPE Ball Brothers Research Corp. of Boulder Colo. PA0 4) MAGNETIC SUSPENSION SYSTEM FOR AN ANNULAR MOMENTUM CONTROL DEVICE, Sperry Flight Control Systems. These references may be found at the REDSTONE SCIENTIFIC INFORMATION CENTER located on Redstone Arsenal, a military installation in Huntsville, Ala.
While the use of gyroscopic masses for stabilization purposes is well known, Applicant is unaware of any effort to use a gyroscopic mass to effect rotary movement of machine tools. Here, advantages are believed to be numerous, and include elimination of flexure of the mount of a machine tool by powering a rotary member mounted thereto without the power source being coupled to the mount. As such, the mount does not receive any reaction forces from the power source during rotation of the rotary member, but serves merely as a pivot for rotation. As a result, the base and supporting structure for the rotating member may be constructed using less weight, with less attendant cost. Also, machining accuracy should increase due to greater closed loop positional control of the rotating member. Further, it is believed that undesirable vibrations that typically cause "chatter" during a machining operation would be dampened by the gyroscopic mass.
A primary operational feature of the invention is the fact that ability to produce torque on a rotating member using a gyroscopic mass is dependent on two variables, namely rate of gimbal movement and momentum of the gyroscopic mass. For larger momentum values, small gimbal rates produce significant precession torques, which may be used to move the rotating member through large excursions with small reaction torques from gimbal movement applied to the rotating member. These small gimbal rates may be achieved using linear actuators, such as solenoids, which simplify control schemes. Another advantage is that since the rotating member typically rotates in a horizontal plane, and the linear actuator produces gimbal motion against the rotating member in a vertical plane, no cross-coupling of these forces occurs. As a result, reaction forces of the linear actuator against the rotating member should not act as a disturbance input in the arm control scheme. Yet another advantage of the present invention is that the gyroscopic mass, when undisturbed, maintains a fixed orientation of the rotatable member without applying reaction forces to the mount or base of the machine. This is superior to conventional servo systems, which when held stationary apply reaction forces to the base, causing loss of machining accuracy.
In accordance with the foregoing, it is a broad object of the invention to provide a power source for a rotating member mounted to a pivot to enable rotation of the member with little or no reaction forces from the rotating member applied to the pivot. It is another object of the invention to provide machine tools, such as a swinging arm robot, wherein precession of a gyroscopic mass is used to provide rotational energy so that little or no reaction forces from such rotation are generated, increasing accuracy and efficiency of machining operations. Other objects and improvements Will become apparent upon reading the following appended specification.